Gear pump



I 'Api-il 12, 1960 D. s. BOOTH ETAL 2,932,254

GEAR PUMP Filed May 2, 1955 2 Sheets-Sheet 1 INVENTORS DOUCLAS GERHARDBOOTH. ROBERT SPVRGEON wool).

' A-r-rorauev April 9 D. G. BOOTH ETAL 2,932,254

GEAR PUMP Filed May 2, 1955 2 Sheets-Sheet 2 INVENTQQS DOUGLAS GERHARDBOOTH, ROBER RGEON W0 D.

was! $7 BY ATTORNEY GEAR PUMP 4 Claims. (Cl. 163-426) This'inventionrelates to gear pumps. A gear pump with which the present invention isconcerned comprises a housing including twochambers which accommodatetwo inter-meshing, displacing gears.

Gear pumps have the advantage of simplicity of construction, butsatisfactory operation at high delivery pressures can be achieved onlyby careful mechanical design, as the volumetric efficiency of such pumpstends to fall as the fluid pressure across the sealing faces, and hencethe leakage, is increased.

Volumetric efficiency can be increased up to a point by machining thepump parts to a high degree of accuracy, but the improvement therebyattained is limited by the fact that the less the clearance employedbetween relatively moving parts the greater is the danger of the pumpseizing in operation. Also, a pump having very small working clearancesis unlikely to have a long working life and is liable to deterioraterapidly in efficiency. I Some of the problems of design of gear pumpshave been solved by pressure loading; in a pressure loaded pump thesealing member between the side faces of the gears and the adjacentstationary part defining the chamber is improved by loading that memberagainst the gear face by a pressure which is related to the deliverypressure of the pump and hence to the pressure within the chamber. Withaccurate mechanical design, pressure loaded pumps can be usedsuccessfully with liquids of comparatively high viscosity such, forexample,'as lubricating oils and fluids used in hydraulic transmissionor control systems.

A new order of difliculty arises where it is desired to design a gearpump for use with fluids of low viscosity, such as kerosene or gasoline,even where the pressure involved is low in comparison with deliverypressures which can be achieved in gear pumps for high viscosityliquids.

The design of a gear pump which is efiicient when used with lowviscosity fluid at high delivery pressures is a problem of greattechnical difficulty, and one which, so far as we are aware, has nothitherto been successfully achieved.

It is, therefore, an object of the present invention to provideimprovements in gear pumps which, while they can be applied to gearpumps generally to improve their 'efficiency, can be used to produce aneffective pump for low viscosity liquids. I

We have 'discoveredthat the low efficiency of hitherto known gear pumpsfor low-viscosity liquids, especially at high pressures, is due to aconsiderable extent to the fact that the pump housing becomes distortedby the pressure, thereby creating undesirable bearing friction.

Therefore a further object of the invention is to provide a gear pump inwhich effective sealing on or against the side faces of the gears isobtained by pressure loading, and in which the loss of efficiency of thepump due to distortion of the pump housing is minimised.

Another object of the'invention is to provide a gear pump in which thebearings are so mounted that mis-v States Patent 2,932,254 Patented Apr.12, 1960 ice that side members and bearings are relatively movable bothlongitudinally and transversely of the journal axes.

-A related feature of the invention is that the bearings are mounted inthe housing so as to be self aligning on the shafts; specifically, saidbearings are mounted in the housing by engagement over an axial lengthwhich is less than the axial length of engagement between the bearingsand the shaft and which is centrally disposed between the ends of thesaid latter axial length.

In carrying the present invention into effect it is advantageous toprovide a reinforced sealing member on the outer faces of the sidemembers for effecting high pressure and low pressure zones; the highpressure zone being in contact with fluid at high pressure from theoutlet side of the pump and the low pressure zone receives fluid at lowpressure from the inlet side of the .pump. In this way, the centre ofpressure acting on the outer faces of the side members can be broughtinto sub stantial alignment with the centre of pressure acting on theinner faces of said side members.

The sealing means preferably consists of an endless flexible memberwhich surmounts a rigid member of less thickness than the depth of saidchamber and having a profile conforming to one of the pressure zones.

Features and advantages of the invention will also appear from thefollowing description of embodiments thereof, given by way of exampleonly, in conjunction V with the accompanying drawings in which:

Fig. 1 is a sectional elevation of a gear pump provided with bearingassembly in accordance with the invention,

Fig. 2 is a view in section on line 2-2 of Fig. 1,

Fig. 3 is a view in section on line 33 of Fig. 1,

Fig. 4 is a view in section on line 44 of Fig. 1,

Fig. 5 is a view in section of line 55 of Fig. 1, and

Fig. 6 is a detail of an alternative bearing support.

Referring to Figs. 1 to 5 of the drawing, a pump housing 1 is providedwith two overlapping cylindrical chambers 2 and 3 having end covers 4and 5 on each end thereof, the end covers being held tightly against theend faces of the housing by bolts, not shown.

A pair of gears 6, 7 which mesh in the overlapping cylinders 2 and 3 areprovided with axially extending journals 8, and side plates 14 havingclearance bores 8a for the journals 8 are inserted in the housing incontact with the outer faces of the gears 6, 7 to form end walls of thepump chambers.

Housing plates 11 located within the housing 1 are provided forreceiving the bearing bushes 9 for supporting the journals 8. Saidbushes 9 are a slide fit in the housing plates ill but are held againstrotation by means of keys 12 fitted into slots 13 in the housing plates11. The housing plates 11 support the bushes 9 at a distanceapproximately midway along the length of the journals 8 and the width ofsaid plates 11 at the point of contact with the bushes 9 is less thanhalf the length of said bushes 9.

A chamber A is formed between the respective outer faces of the sidesplates 14 and inner faces of the housing plates 11. Each chamber A isdivided in two zones or chambers 15, 16 (Fig. 3) by means of areinforced sealing member, and said side plates 11 are urged towards thegears 6 and 7 by a side load derived from the pressures in the separatezones of chambers 15, 16.

With the direction of rotation of the gears 6, 7 as indicated by thearrows in Fig. 4, 17 is the inlet port and 18 is the outlet port.

The sealing members each consist of an endless flexible ring 19 whichsurrounds the low pressure chamber 16 and is adapted to be sealinglycompressed between the outer faces of the side plates 14 and housingplates 11 to isolate the two chambers 15, 16.

A separate pressure relief plate 20 of less depth than chamber 16 isprovided to prevent each ring 19 from collapsing and has a configurationconforming to the peripheral shape of the low pressure chamber 16 whichis bounded by the ring 19; and a guide plate 30 fixed to the housing inthe high pressure chamber 15 assists in maintaining the shape of thering as shown in Fig. 3.

The pressure relief plates 20 are provided with a port 23 adjacent theinlet 17 for the admission of low pressure fluid into the chamber 16 andthe plate 30 has a similar port 31 adjacent the outlet port for theadmission of high pressure fluid into the chamber 15.

The side plates 14 each have an opening 25 in line with the inlet port17 and outlet port 18 respectively for the purpose of admitting fluidthrough the ports 23, 31.

Passageways or grooves 21 are provided in the side plates 11 (Fig. whichcommunicate with the low pressure inlet 17 for the circulation of lowpressure fluid through the helical groove 24 in the bearing bushes 9 onthe low pressure side of the journal bearings. This will produce acirculation of the pump liquid to lubricate and cool the bearings due tothe pumping effect of the relative movement of the journal and thebearing grooves, the static pressure in the chambers at the outer endsof the bearings being the same as at the inner ends due to theirconnection to the low pressure chamber 16. V

The side plates 14 and pressure relief plates 20 are provided withcoinciding apertures for receiving dowels 32 whereby the said reliefplates 20 can be easily located clear of the journals 8.

In the pump of the present invention, the effects of distortion areovercome firstly by making the bearings for the gear journals separatefrom the pressure loaded members engaging the sides of the gears.Thereby it becomes possible to accommodate the relative movements of theshaft and side members. Secondly, the bearings for the journals aremounted in the housing so that they can adapt themselves to themisalignment of the journals, due to the flexing. The necessary movementis small and in the embodiment of the invention described is provided bysupporting the bearing bushes over a limited length of surface at 10,this surface being approximately centrally between the axial length ofengagement of the bush with the journal. With such an arrangement thedesired latitude of movement of the bush in the housing can be obtainedwithout recourse to non-cylindrical engagement surfaces and withoutusing a large clearance at the engaging surfaces 10.

It is also to be understood that the pressure areas of the side platesof the pump are accurately determined, so that the requisite degree ofbalance 'is obtained to secure proper sealing without excessive load,which may cause seizure.

In this connection it is advantageous to ensure that the centre ofpressure loading coincides with the centre of pressure on the sideplates tending to causing unloading, so that'the optimum sealing of theside plates with minimum end load is ensured.

The embodiment of the invention shown in Fig. 6 is generally similar tothat described above, except that the support for the bearing bushes 9is formed as an integral part of the cover 5 by providing bores 34 forreceiving the bearing bushese 9 as an alternative to having separatehousing plates as herein described with reference to Fig. 1.

The keys 12- are fitted into slots in the end cover 5 to maintain theangular position of said bushes 9 It will be apparent to those skilledin the art that modifications can be made to the pumps described above,which are to be taken as illustrative only, without departing from thespirit of the invention as defined by the scope of the following claims.

We claim:

1. A gear pump having an inlet and an outlet and comprising a housinghaving therein two chambers, two inter-meshing displacing gears mountedfor rotation in said chambers, said gears each having journals extendingaxially therefrom, bearings engaging said journals over an axial lengththereof, means for supporting said bearings in said housing, saidsupporting means only engaging each bearing over a portion of the axiallength of said hearing which is intermediate the ends of the bearing andhas an axial length less than half the said axial length of the bearing,while on the remainder of its axial length the bearing is unsupported soas to permit alignment of the bearings on said journals, side memberseach having two oppositely facing side surfaces one of which engages theside faces of said gears, said side members being mounted in saidhousing for limited movement in a direction axial of said journal andhaving bores through which said journals extend with radial play, andmeans for applying output fluid pressure to a predetermined area of theother side surface of at least one of said side members.

2. A gear pump according to claim 1 and comprising housing platesmounted in the housing and supporting the bearings.

3. A gear pump according to claim 1 and comprising end covers for saidhousing, said end covers supporting said bearings.

4; A gear pump having an inlet and an outlet and comprising a housinghaving therein two chambers, two intermeshing displacing gears mountedfor rotation in said chambers, said gears each having journals extendingaxially therefrom, bearings engaging said journals over an axial lengththereof, means for supporting said bearings in said housing, said meansengaging each said bearing over an axial length of said bearing which isintermediate the ends of and equals less than half the said axial lengthof the journal bearing While the bearing is unsupported on the remainderof its axial length, so as to permit alignment of said hearings on saidjournals, side members each having two opposite side surfaces one ofwhich engages the side faces of said gears, said side members beingmounted in said housing for limited movement in a direction axial ofsaid journals and having bores through which said journals extend withradial play, and means for applying output fiuid pressure to apredetermined area of the other side of each said member and comprisingmeans for defining a high pressure area and a low pressure area on atleast one of said members, whereby the centre of pressure on said sidemembers coincides with the centre of pressure on said gears.

References Cited in the file of this patent UNITED STATES PATENTS185,188 Pickering Dec. 12, 1876 385,288 Turner" u June 26, 1888 489,505Silvey Jan. 10, 1893 1,771,863 Schmidt July 29, 1930 2,040,754 McLeodMay 12, 1936 2,044,873 Beust June 23, 1936 2,487,732 Schanzlin Nov. 8,1949 2,527,941 Lauck et al. Oct. 31, 1950 2,641,192 Liudberg' June 9,1953 2,672,100 Harvey Mar. 16, 1954 2,682,836 Orr, Jr. July 6, 1954(Other references on following page) 5 UNITED STATES PATENTS ComptonNov. 30,1954 Drennen May 3, 1955 Kane Aug. 9, 1955 Booth et a1 Feb. 21,1956 Eames May 21, 1957 Miller et a1. Oct. 15, 1957 Jarvis Dec. 17, 19576 Compton Feb. 25, 1958 Banker Feb. 25, 1958 FOREIGN PATENTS GreatBritain a. May- 26, 1938 France Nov. 28, 1939 France Nov. 28, 1939France Mar. 2, 1955

